From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id D7E17271443; Wed, 23 Sep 2026 15:10:03 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790176205; cv=none; b=R3VS73qUjdVOUZOEq/XPc6uQZKehQNnIaTiKAPWGVKyDvEE3hl8FoQqdBP+zF6DgbV35VUW6SRLpoPeCCF0+pTet/dBHrB9Dyb1WpP7V94c0fC5SvngQHjYyJXPn+n6Dgushn+8lUwLwCbunndM3LLrqtBTEU7pv1ndyH7VFavI= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790176205; c=relaxed/simple; bh=ZsCiCgubVfsHQuLEBzKfRq8LU4r2cNza4kmPyv0Ar34=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=eWYQ1eJOqAm7JqjbaOwFU0G0XpEyfO9X5Q22TRtlERn0KwcizAGZY/zEJJxr/6HnLRWGfF6kVM/1esjRvA/Tu9yGIsWmG9weniV2Ec26yz+SsNQuUAw3L4Ugr1ql4BN/8yAmD0toQalX6iEODizHoxQQEklk42SjXjvey6bBuc8= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=A9k+J1Xv; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="A9k+J1Xv" Received: by smtp.kernel.org (Postfix) with ESMTPSA id F41101F00898; Wed, 23 Sep 2026 15:09:59 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1790176203; bh=4tUYPNtyNh01xCJ2PLgysU7v0U9kxuU1XJhtJwMfEio=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=A9k+J1Xv8H8FlYMbCo5VEee282+QP0qM1mxPpKCknxblZba3vik10szV2Grl23HTF OdhkfcRQhNcFuksIR073l7cXQs4kpB7X1qLbpYCwRbNmIWM9sxWl7Z2M2i5sR5/xc6 VlxeK+yTWZ5D9aHtmwk2TvDkw72If4pGYi5TjFz/86tLcnf7cVcx9tK2Xml/jmlYUb nXbGKtqEwSAT/JuuCAT7PpIRv0RrHdbNgOCBhQwgAn2wJkd7slhonzJLo7MLfL/L41 AHWGPU7pjxW/DUxdkyGj8W8oE07LvQ9J7aGlXtGzBkE4/L0M6uOwRmDqRbAgTWCvvg Z8xvUoLdf0GXQ== Message-ID: <1857df9a-8952-426e-988b-cd05d45a04cc@kernel.org> Date: Wed, 23 Sep 2026 17:09:57 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC PATCH] fpga: region: Add support for FPGA region variants To: Marco Pagani , Xu Yilun Cc: Moritz Fischer , Xu Yilun , Tom Rix , linux-fpga@vger.kernel.org, linux-kernel@vger.kernel.org, Rob Herring , Saravana Kannan , Krzysztof Kozlowski , Conor Dooley , devicetree@vger.kernel.org References: <417b510f-0f6d-4695-97f5-3fc19b9377b9@linux.dev> <9d4af487-69a7-4a0d-9335-35c3a057de54@linux.dev> <4dbdb52e-1b28-432e-a3a7-ad9c44f17d27@linux.dev> <8848432d-45b0-4efe-adf3-adfb64fe0899@linux.dev> <11b1a792-f8b1-4fce-8a7a-8352149febcf@linux.dev> <2adefc6f-328c-4683-8cba-091d9f3425ab@linux.dev> From: Krzysztof Kozlowski Content-Language: en-US Autocrypt: addr=krzk@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit On 23/09/2026 16:30, Marco Pagani wrote: > > > On 18/09/2026 19:36, Xu Yilun wrote: >> On Fri, Sep 18, 2026 at 05:07:07PM +0200, Marco Pagani wrote: >>> >>> Hi Yilun, >>> >>> Is it okay with you if I CC the DT people to ask for an opinion? >> >> Of course. It's good to know in which case could a DTO be applied. >> >> But to be clear, I think that only affects how we accept and apply the >> image-DTO pair. For now, I basically don't want a varient selection >> interface. > > > Hello Rob, Saravana, Krzysztof, Conor, > > I'm CC-ing you on this thread as OF/DT maintainers to kindly ask > for your input on this debate we are having about how to implement > userspace FPGA reconfiguration, an important feature currently > lacking in mainline kernel. > > https://lore.kernel.org/all/20260608164247.1998417-1-marco.pagani@linux.dev > > To recap: modern FPGAs allow portions of the fabric to be reconfigured > at runtime to dynamically swap soft IPs. Usually, these IPs are > connected through a non-discoverable on-chip bus like AMBA AXI. > From a kernel perspective, this means the FPGA device configuration > image (bitstream) must be paired with a DT fragment that describes > the new topology. > > In this thread, we are essentially debating between two approaches for > implementing FPGA userspace reconfiguration at runtime: > > - Statically defined Variants (this RFC): Userspace can change FPGA > configuration by selecting from a pre-validated set of variants > (DT fragments) baked into the base DT. I don't know what DT fragments are, maybe you meant overlays? But they are not baked into the base DT. There are no bindings here and no DT maintainers were CCed on this RFC, so I really do not get how this patch can enable something like that. Linked URL shows some undocumented ABI, so obviously this would be a no go. And RFC prefix does not justify undocumented ABI. At least one without clear explanation in the cover letter, why is this RFC and why it cannot be merged/reviewed. > > - Runtime DTOs (Nava's RFC): Userspace can change FPGA configuration > by loading DTOs that are validated at runtime. If runtime overlays were working, this looks suitable to the problem of runtime change of the hardware. This also fits hot-pluggable hardware problem, which Bootlin is working on. Best regards, Krzysztof